The density of a debris flow is far higher than the density of a water flow, and the fluidic dualistic structure of the debris flow, which contains clastic soil, has particularity and shows the characteristics of high inertia, strong transport force, and huge impact force. Due to the severe erosion produced by debris flow movement, a gully bed undergoes severe changes that can cause bottom tearing of the gully bed and the collapse of a gully bank, adding solid matter sources that replenish the debris flow, thereby increasing the damage it causes. Drainage channels are among the main engineering measures for the prevention and control of debris flows, and the reasonable planning of debris flow drainage channels has great social, economic and ecological environmental significance for reducing the destructive power of debris flows and improving the safety of downstream protected objects.
Under the influence of factors such as the interaction of mountainous terrain, a debris flow gully and a main river, for example, a debris flow-deposited fan for constructing a drainage channel may be very long, at over 1000 meters, or very short, at only approximately 100 meters. For debris flow-deposited fans with different lengths, the reasonable planning of debris flow drainage channels is key to effectively preventing and controlling debris flows and protecting any protected objects on the deposited fans.
Currently, a debris flow drainage channel generally includes an inlet section, a main channel section and an outlet section in the drainage channel plane. The channel types of the three sections are the same, mainly a fully lined type and a transversely penetrated notched sill type. The integrally single channel type structure easily causes problems that the flow velocity of the debris flow at the upper end of the main channel increases too slowly and the flow velocity of the debris flow at the lower end of the main channel is too fast, so that the upper end of the drainage channel is deposited and the downstream part of the drainage channel is eroded. On the other hand, for a long accumulated fan (length over 300 meters), currently, the same drainage channel is adopted to drain the debris flow generally, which causes defects because it is difficult to adapt the drainage channel to the great changes in the longitudinal slope of a gully bed in a long deposited fan. As a result, the upper end of the drainage channel is eroded and the lower end of the drainage channel is deposited. An overlong drainage channel is not beneficial to the stability of a entire drainage system. For example, after the upper end of a fully lined drainage channel with a length of 750 meters at the Shiwei River in Yunlong County of Yunnan Province was subject to bottom tearing, chain bottom tearing of the drainage channel occurs, and consequently the entire channel was destroyed.